A fuel cell system generally includes fuel cells and diversity of auxiliary machinery related to the operations of the fuel cells. The auxiliary machinery include a pump driven to supply a fuel gas required for the operation of the fuel cells, an air compressor driven to supply an oxidizing gas required for the operation of the fuel cells, a cooling water circulation pump driven to control the temperature of the fuel cells, and sensors used to detect the voltage, the temperature, and any other suitable parameters of the fuel cells. The power supply to such auxiliary machinery is accordingly essential at the time of the operations of the fuel cells.
One proposed fuel cell diagnosis device is designed to measure a resistance of fuel cells in an IG-on (ignition-on) condition and subsequently start power supply to a motor (see, for example, Japanese Patent Laid-Open No. 2005-332702, No. 2007-128778, No. 2004-179003, No. 2003-45467, and No. 2007-66643). There is accordingly a requirement for supplying electric power to a sensor used for measuring the resistance of the fuel cells in the IG-on condition.
On a start of the fuel cell system, it is required to supply electric power to the auxiliary machinery related to the operations of the fuel cells. The electric power for the auxiliary machinery is supplied from a power source other than the fuel cells, for example, an electricity storage device such as a low-voltage battery. When there is a long standby time before an ON operation of a start switch (an actual start of the fuel cells) during the measurement of the resistance of the fuel cells in the IG-on condition as disclosed in the above cited patent documents, a large amount of electric power stored in the low-voltage battery is consumed. This leads to a potential for insufficient power supply to the auxiliary machinery on a start of the fuel cells. There would thus a requirement for reducing the power consumption before a start of fuel cells.